1. Field of the Invention
The present invention relates to a liquid crystal display device and, more particularly, to an active matrix type liquid crystal display device of a thin film transistor (TFT) type or the like.
2. Description of the Related Art
Liquid crystal display devices, because of their features such as thin size, light weight and low power consumption, are widely used as display devices for image information and character information in information equipment represented by personal computers, mobile types of information terminals, mobile telephones, and visual equipment such as digital cameras and camera-integrated type VTRs. In recent years, the fusion of personal computers and video digital media has proceeded owing to the appearance of DVDs, the popularization of large capacity media resulting from the rapid evolution of large-capacity magnetic disk drives, and the start of BS digital broadcasting, so that demands for display devices of higher image quality capable of coping with such uses have been stronger and stronger. Since these display devices also premise uses in TVs, it has been demanded that such display devices have brighter screen displays. Accordingly, backlights (BL) to be used in the display devices are becoming brighter and brighter.
In the field of liquid crystal display devices for use in applications of high image quality, two kinds of modes are mainly used: a vertical electric field mode in which an electric field is applied in the vertical direction of a substrate, as represented by an TN type and an MVA type; and a lateral electric fieldmode in which an electric field is applied in the horizontal direction of a substrate, i.e., a so-called in-plane-switching (IPS) mode.
In the IPS mode of liquid crystal display device, it is general practice to use a storage capacitance formed of an insulating film between a pixel electrode and a counter electrode on a substrate on which TFTs are formed, as disclosed in Japanese Patent Laid Open No. H07-36058.
In the vertical electric field mode of liquid crystal display device as well, it is known that a storage capacitance is formed of an insulating film between a pixel electrode and a storage capacitance signal line on a substrate on which TFTs are formed.